Faulting and Magmatic Accretion Across the Overlapping Spreading Center Between Vance Segment and Axial South Rift, Juan de Fuca Ridge

Plate divergence along mid-ocean ridges is accommodated through faulting and magmatic accretion, and, at overlapping spreading centers (OSC), is distributed across two curvilinear overlapping ridge axes. One-meter resolution bathymetry acquired by autonomous underwater vehicles, combined with distribution and ages of lava flows, is used to: (a) analyze the spatial and temporal distribution of flows, faults, and fissures in the OSC between the distal south rift zone of Axial Seamount and the Vance Segment, (b) locate spreading axes, (c) calculate extension, and (d) determine the proportion of extension accommodated at the surface by faults and fissures versus volcanic extrusion over a period of similar to 1300-1450 years. Our study reveals that in the recent history of the ridges, extension over a distance of 14 km across the Axial/Vance OSC was asymmetric in proportion and style: faults and fissures across 1-2 km of the Vance axial valley accommodated similar to 3/4 of the spreading, whereas dike-fed eruptions contributed similar to 1/4 of the extension and occurred across 4 km of the south rift of Axial Seamount.